$-8rs + 6rt + 3r - 7 = -7s - 6$ Solve for $r$.
Answer: Combine constant terms on the right. $-8rs + 6rt + 3r - {7} = -7s - {6}$ $-8rs + 6rt + 3r = -7s + {1}$ Notice that all the terms on the left-hand side of the equation have $r$ in them. $-8{r}s + 6{r}t + 3{r} = -7s + 1$ Factor out the $r$ ${r} \cdot \left( -8s + 6t + 3 \right) = -7s + 1$ Isolate the $r$ $r \cdot \left( -{8s + 6t + 3} \right) = -7s + 1$ $r = \dfrac{ -7s + 1 }{ -{8s + 6t + 3} }$